The present invention concerns a novel parenchymal cellulose and a process for its production. More particularly, the present invention concerns a novel microfibrillated cellulose and a process for its production from primary wall plant pulp, particularly from sugar beet pulp after extraction of saccharose.
Cellulose is a substance of great industrial importance which has numerous applications, including:
alimentary applications as a thickener to stabilize dispersions, emulsions and suspensions, for low calorie food products, low fat or low cholesterol food products, etc; PA1 industrial applications, in paints, paper, textiles, agriculture, cosmetics, etc; PA1 pharmaceutical applications, such as an excipient for medication, a precipitation control agent, ointment or cream support, intestinal transport agent, etc. PA1 15% to 30% cellulose; PA1 12% to 30% pectins; PA1 12% to 30% hemicelluloses; PA1 2% to 6% proteins; PA1 2% to 6% mineral materials; PA1 2% to 6% lignin, tannins, polyphenols and ferulic ester. PA1 suspending the sugar beet pulp in an acidic (pH&lt;4.5) or basic (pH&gt;10.0) aqueous medium; PA1 heating the suspension to a temperature of more than 125.degree. C. (0.5 MPa); PA1 keeping the suspension at a temperature of more than 125.degree. C. for a period of between 15 seconds and 360 seconds; PA1 subjecting the heated suspension to mechanical shearing in a tube reactor followed by rapid depressurization through small orifices into a zone which is at atmospheric pressure; PA1 filtering the suspension and recovering the insoluble fraction which contains the parenchyma cellulose and the soluble fraction (filtrate) which contains the hemicelluloses; PA1 treating the cellulose fraction by bleaching with sodium hypochlorite and mechanical defibrlllation to produce a parenchyma cellulose paste constituted by cell wall fragments. PA1 (a) acid or basic hydrolysis of the pulp partially to extract the pectins and hemicelluloses; PA1 (b) recovering a solid residue from the suspension from step (a); PA1 (c) carrying out, under alkaline conditions, a second extraction of the residue of cellulosic material from step (b), this step being obligatory if step (a) is acidic and optional if step (a) is basic; PA1 (d) if necessary, recovering the cellulosic material residue by separating the suspension from step (c); PA1 (e) washing the residue from step (b) or step (d); PA1 (f) optionally, bleaching the cellulosic material from step (e); PA1 (g) recovering the cellulosic material by separating the suspension from step (f); PA1 (h) diluting the cellulosic material from step (g) in water to obtain between 2% and 10% of dry matter; PA1 (i) homogenizing the cell suspension from step (h); characterized in that PA1 (j) step (a) is carried out at a temperature between about 60.degree. C. and 100.degree. C., preferably between about 70.degree. C. and 95.degree. C., more preferably at about 90.degree. C.; PA1 (jj) at least one alkaline extraction step (a) and/or (c) is carried out on the cellulosic material, salid alkaline extraction being carried out with a base, preferably selected from caustic soda and potash, the concentration thereof being less than about 9% by weight, preferably between about 1% and 6% by weight; PA1 cellulose I.fwdarw.cellulose II PA1 unique Theological properties such that stable suspensions can be produced at pHs in the range 2 to 12 and in a temperature range of 0.degree. C. to 100.degree. C. at a minimum concentration of 0.2% and with the appearance of a gel at concentrations of more than 1%. PA1 unique physical and chemical properties in that the cellulose is mainly constituted by cellulose associated with a residual amount of pectins or hemicelluloses which procure particular physical and chemical properties. The cellulose of the invention is constituted by microfibrils of the native or cellulose I type which are separated out to a greater or lesser degree. PA1 very high chemical reactivity, very large accessible surface area; PA1 excellent water retentive capacity; PA1 high suspending capacity; PA1 thickening capacity. PA1 for paints, it constituted a good thickening agent in the aqueous phase, and can replace hydroxy-propyl-celluloses, for example; PA1 its film-forming and strengthening properties can be used in latex for paints, paper, adhesive coatings, etc. PA1 as a thickening agent which can be used in drilling muds. PA1 using the strengthening properties of microfibrillated cellulose by introducing it into the paper pulp; PA1 combined use of the thickening, strengthening and film-forming properties of microfibrillated cellulose to coat certain special papers. The cellulose also has beneficial barrier properties. PA1 microfibrillated cellulose can stabilize emulsions, act as an aroma support, a gelling agent and especially as a thickening agent; PA1 it can replace or act in synergy with other thickening agents already used in this field, such as xanthane, CMCs, or microcrystalline celluloses.
Until now, all known celluloses have had disadvantages.
WO 93/11182 from Weyerhaeuser describes a bacterial cellulose with a reticulated structure. Apart from being very expensive, such a bacterial cellulose can cause contamination problems in alimentary applications.
FR-A-2 472 628 from ITT INDUSTRIES describes a microfibrillated cellulose essentially constituted by secondary walls obtained from wood pulp. Such a cellulose cannot easily be taken up into suspension once dehydrated. this causes considerable storage and transport problems due to the fact that the suspensions have a maximum cellulose content of about 4%.
In attempting to overcome that disadvantage, EP-A-0 120 471 from ITT INDUSTRIES describes a redispersable dried secondary wall (since it is obtained from wood pulp) microfibrillated cellulose which is characterized by the presence of an additive which prevents the formation of hydrogen bonds between the cellulose fibrils. The quantity of additive is considerable (at least 50% by weight with respect to the cellulose, and preferably at least the same quantity thereof). The additive is, for example, a polyhydroxylated compound such as a sugar containing 5 to 6 carbon atoms or a glycol, a borate or an alkaline phosphate, an aprotic solvent, an amine or a quaternary ammonium compound. Apart from the fact that the designation "cellulose" is improperly assigned to a product which is at most half cellulose, this "cellulose" is costly and is not suitable for all applications. Further, without the addition of additives this cellulose can only recover from 2% to a maximum of 20% of its initial viscosity after drying. Maintaining the viscosity requires the presence of an additive in an amount by weight which is substantially the same as that of the cellulose.
EP-A-0 102 829 from Weibel describes a process for simultaneously isolating the cellulosic and hemicellulosic constituents of sugar beet pulp. However, as with FR-A-2 472 628 cited above, once dehydrated, the parenchymal cellulose obtained cannot readily be taken up again into suspension, causing the same storage and transport problems.
Further, the economic exploitation of plant residues, in particular sugar beet pulp, is of great industrial importance.
One aim of the present invention is to provide a microfibrillated cellulose which can be taken up into suspension after dehydration without adding an additive.
Another aim of the invention is to provide a microfibrillated cellulose which regains almost all of its initial viscosity after drying, without adding an additive.
A further aim of the invention is to provide a process for the production of cellulose by economic exploitation of primary wall plant residues, in particular sugar beet pulp.
The present invention achieves all these three aims.
Further aims and advantages of the invention will become apparent from the description below.